A bayonet coupling of this kind is known from DE 43 07 539 A1.
In medical technology, there is an increasing demand for instruments, and in particular for tubular-shaft instruments, which can be disassembled with a few actions in order to clean and sterilize the instruments after an operation. In addition, modular designs have gained a foothold in medical technology; for example, a variety of instrument parts such as blades, gripping forceps, or the like can be mounted on at the distal end on tubular-shaft instruments having scissor-like handles.
In minimally invasive surgery, it is often necessary to insert an endoscope, a trocar, a forceps, a scissors, or another instrument into a shaft which can, for example, be a universal shaft, a trocar sleeve, or the like. It is necessary in this context that the instrument joined to the shaft be immovably joined to the shaft during use, and that it be easily capable of being detached again when necessary.
A coupling is provided in order to create this immovable join. These couplings are generally configured as bayonet couplings, i.e. a bayonet sleeve (female part) having a bayonet guide is provided on one of the tubular-shaft instruments or instrument parts, and a bayonet insert (male part) is inserted or twisted into this.
Interlock systems are provided so that the bayonet coupling is not disconnected during handling by rotation of the coupled parts relative to one another.
In the case of DE 43 07 539 A1 cited initially, the bayonet sleeve is provided at the distal end of a tubular shaft of a forceps. The bayonet insert is provided at the distal end region of a rod-shaped actuation element that carries the forceps jaw parts at the distal end. The proximal end of the rod-shaped actuation element is used for joining to a movable grip element of the handle, which is scissor-like or configured otherwise. When these two parts are coupled, the proximal end of the rod-shaped actuation element is pushed distally into the shaft and through it until the bayonet insert comes into engagement with the bayonet sleeve. Once the bayonet insert has been slid into the bayonet guide of the bayonet sleeve and rotated, the two components are interlocked in this position. For this, there are provided at the proximal end of the rod-shaped actuation element two axially extending flattened areas, into which are recessed radial clamping elements which are held in the clamping position by means of a spring washer. The clamping elements prevent any relative rotation between shaft and rod-shaped actuation element.
This interlock system is cumbersome to handle, and requires dimensionally accurate machining of the draw-in bar and the sleeve at the proximal end.
Because the actual bayonet coupling is arranged at the distal end, but the interlock system is at the proximal end of the tubular-shaft instrument, torques acting on the tubular-shaft instrument can nevertheless cause loosening of the coupling. The rod-shaped actuation element has, with ordinary forceps, diameters in the range of a few millimeters, but lengths in the range of 20 cm and more. In other words, the coupling is located at an axial distance of approximately 20 cm from the interlock system. Torques can now cause torsion of the long, thin rod-shaped actuation element such that the distal end of the rod is rotated sufficiently, relative to the locked proximal end, for the coupling to release.
Torques of this kind act on instruments when a piece of tissue, for example cartilage, is grasped with, for example, the instrument part operating at the distal end, and the intention is to detach the piece of tissue being grasped by closing and rotating the instrument.
DE 43 23 093 A1 discloses a similar surgical forceps in which the bayonet coupling is also provided at the distal end, and the interlock system at the proximal end. The interlock system is carried out in such a way that at the proximal end of the rod-shaped actuation element, an axially extending spring element is provided, which snaps into a longitudinal slot at the proximal end of the shaft. Here again, torsion of the rod-shaped actuation element can cause the coupling to release.
Such release can have fatal consequences for the patient, since the instrument can then no longer be actuated, and comes apart into two pieces inside the patient's body.